N-Doped Porous Carbon-Supported Cu₂O Active Sites for Electrochemical Nitrate Reduction to Ammonia

Ammonia (NH₃) is a vital chemical and a promising carbon-free energy carrier. Electrochemical nitrate reduction reaction (NO₃RR) offers an environmentally friendly alternative for NH₃ production, but its efficiency is often limited by sluggish kinetics and competing hydrogen evolution. This work presents a one-step calcination process for the preparation of cuprous oxide supported on nitrogen-doped porous carbon (Cu₂O/NPC) using copper citrate, potassium citrate, and urea as precursors. The resulting Cu₂O/NPC catalyst exhibits a remarkable NH₃ yield rate of 9.43 mg h^-1 mg_cat.^-1 and a Faradaic efficiency of 98.13% at -0.67 V vs RHE, superior to most previously reported Cu-based catalysts. A series of characterizations confirm that the synergistic effect of N-doped carbon and Cu₂O leads to optimized electronic structure, enhanced interfacial charge transfer, and stabilized Cu₂O active sites. EPR and radical scavenging experiments reveal that Cu₂O/NPC can efficiently generate active H species from water splitting, which are preferentially consumed in the NO₃RR to accelerate nitrate to NH₃ conversion. Moreover, the catalyst shows excellent long-term stability, maintaining over 85% of its activity after 20 h of continuous operation. This work provides a sustainable route to design highly active and durable Cu-based catalysts toward efficient nitrate-to-ammonia conversion and environmental remediation.